Accompanying increases in the performance of focal point detecting devices in recent years, many focal point detecting means have been proposed that can measure distance at multiple points in the field of view, which is termed multipoint ranging. In addition, phase difference AF is conventionally known as a means of focal point detection. In a focal point detecting means that carries out multipoint ranging by using the principle of phase difference AF, a pair of image signals, which are associated with the respective measured ranging points, is acquired, correlation computation is carried out, and a defocus amount is calculated from the phase difference.
As one method for detecting the focusing state of a camera lens, Japanese Patent Laid-Open No. S58-24105 discloses an apparatus that carries out focal point detection by a pupil-splitting method using a two-dimensional sensor in which a microlens is formed at each pixel of the sensor. The apparatus of Japanese Patent Laid-Open No. S58-24105 is structured such that photoelectric converting units for each of the pixels that form the sensor are spit into a plurality, and the partitioned photoelectric converting units receive light from different areas of the pupil of the camera lens. In addition, Japanese Patent Laid-Open No. S61-18911 discloses a focal point adjusting apparatus that carries out correction when what is termed “vignetting” occurs due to the camera lens. In Japanese Patent Laid-Open No. S61-18911, the illumination and the vignetting state of the lens are associated and stored, and a conversion coefficient, which converts an amount of blur to a defocus amount depending on the state of illumination of the lens while photographing, is corrected. Furthermore, Japanese Patent Laid-Open No. 2004-12493 discloses a focal point adjusting apparatus that calibrates a conversion coefficient that converts a blur amount to a defocusing amount. In Japanese Patent Laid-Open No. 2004-12493, before the operator takes a photograph, a calibration operation is carried out, and this value is stored in the camera. While photographing, the blur amount is converted to a defocus amount by using a calibrated conversion coefficient. Furthermore, Japanese Patent Laid-Open No. 2007-121896 discloses a focal point adjusting apparatus that calculates a conversion coefficient that converts a blur amount to a defocus amount while taking into consideration vignetting that is caused by the camera lens. In Japanese Patent Laid-Open No. 2007-121896, a conversion coefficient, which converts a blur amount to a defocus amount based on the profile of the focal point detection optical system and the aperture information of the camera lens system, is calculated.